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Guest ElStevos

Pc-7 Torque gauge. Analog + Digital

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Gents,As a first time poster I come here in a final attempt to solve a problem I

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(A:ENG1 TORQUE, foot pounds) works and gives the proper value when tested with the Cessna C208B.(A:ENG1 TORQUE, pound-force per square foot) works but,,, IS IT THE RIGHT VALUE ?(A:ENG1 TORQUE, pound-force per square inch) does not work(A:ENG1 TORQUE, pound-force per square foot) 144 * should give the right value for PSI as long as the original value is correct.Hope it helps..... Regards,Roman(KGRB)

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Ron,You are right ... I tried to help ElStevos by trying different (variables,units) that would even show a value. IE to show something. (A:ENG1 TORQUE, pound-force per square foot) 144 * does work and is proportional to (Torque, foot pounds) BUT.... Non of the physics I ever tried could there be a way to convert the two.. IE foot pounds to PSI,PSF etc... Would need another value,, maybe shaft radii??> Baffling. Regards,Roman(KGRB)

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> It sounds like you want BMEP, Brake Mean Effective Pressure>(psi). Which is proportional to torque.>> BMEP is a function of shaft RPM and Shaft Power. Maybe just>Shaft Torque. Off hand, I don't remember the constant>involved. >I found the following code value for BMEP that I am using for now. I don't much like it as I know its likely incorrect, but seems to be the value a couple of others have used.(A:ENG2 TORQUE,foot-pound) 10 /The problem is BMEP, IIRC, is a very poor rating of power as it was created to measure the power of a specific type of engine in Britain way back in the 20's. The problem was that, while a simple formula for that particular engine type, it does not work for other engine types and becomes increasingly inaccurate as values change in figures like bore and stoke, compression rations etc. and was ultimately dropped for more accurate ways of measuring power. It is surprising to see it still used in some AC.The only reason I use it is it give me an indication of relative power. Much like a 3d video benchmark, its not so much to compare my results to other peoples results, but to monitor my own engines performance.I am curious though. In the Pc-7, why would a rotational (twisting) force be measured with preasure values?CheersShad

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>>I am curious though. In the Pc-7, why would a rotational>(twisting) force be measured with preasure values?>Me too.. Just Curious.. A viscous coupling in the gearbox ? ( automotive torque convertor ) Hydraulic pressure would increase as torque increases to stay coupled. Hydraulic constant speed prop ? Hydraulic pressure would increase as torque increases to keep same prop speed. Just thoughts thrown in the air..Curiosity killed the cat.Regards,Roman(KGRB)

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>>>>>I am curious though. In the Pc-7, why would a rotational>>(twisting) force be measured with preasure values?>>>>>Me too.. Just Curious.. A viscous coupling in the gearbox ? (>automotive torque convertor ) Hydraulic pressure would>increase as torque increases to stay coupled. >>Hydraulic constant speed prop ? Hydraulic pressure would>increase as torque increases to keep same prop speed. >>Just thoughts thrown in the air..Curiosity killed the cat.>>Regards,>Roman>(KGRB)LOL. Those reasons sound plausible to me.PS I think from now on I am going to write my post in Word and spell check them first, heheh. Typos are the bane of my existence.CheersShad

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According to "Aircraft Gas Turbine Powerplant" (Jeppesen) the PT6 engine has a first stage planete gear, where the outer ring is able to move slightly on helical splines. So if the engine delivers torque, the outer gear ring is slightly turned due to reaction force. The slight turn is transposed to axial shift, because of the helical splines. So due to torque the first stage moves slightly in axial directon. With the outer ring a small oil valve is also moved and gives a small metering orifice more or less free. This makes the transition from axial movement to oil pressure. This pressure is displayed as torque.I don't know the engine of the Pilatus, but also other gas turbine engines use this or other technique to transform torque to oil press and then display oil press, mainly because the torque is measured on a rotating part and oil press methods don't need to care about rotational pickup (like e.g. electrical measurements, but there are also tricky solution available without pickup problems). Since in the PT6 engine the reaction torque on the gear case is measured, the pickup problems are not that difficult.In difference the Allison 250 turboshaft engine has e.g. an intermediate gear which internal twisting is used as torque measurement, translated to oil press etc. ...Arne Bartels

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>> It sounds like you want BMEP, Brake Mean Effective Pressure>>(psi). Which is proportional to torque.>>>> BMEP is a function of shaft RPM and Shaft Power. Maybe just>>Shaft Torque. Off hand, I don't remember the constant>>involved. >>I found the following code value for BMEP that I am using for>now. I don't much like it as I know its likely incorrect, but>seems to be the value a couple of others have used.>(A:ENG2 TORQUE,foot-pound) 10 / No, that's not BMEP. I think BMEP is defined as Constant * (Shaft_Torque/Displacment). Or, a function of Shaft HP and RPM instead of Shaft_Torque. BMEP is a good measure of combustion stresses on an engine. One might see 100 lb/in^2 in cruise. 300 psi is high, and would probably only be hit in a supercharged engine.>I am curious though. In the Pc-7, why would a rotational>(twisting) force be measured with preasure values?>Cheers>Shad Looks like Arne figured it out. Because oil pressure on a piston is proportional to torque. So, one could scale 'Shaft Torque' to appropriate 'torque psi'. Ron

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Hmm, a quick search turned up the folowing:bmep = Power / ( Swept Volume x revolutions per second)Orbmep = 2 x Pi x Torque / (Swept Volume)"Bmep is a useful comparitor of engine performance and state of tune, although, care must be taken to consider the rpm at which the engine is operating to determine the power potential."http://www.factorypipe.com/Technical/Tech_.../BMEP/bmep.htmlLooks like I'll be changing my guage formula heheh.CheersShad

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>Hmm, a quick search turned up the folowing:>>bmep = Power / ( Swept Volume x revolutions per second)>Or>bmep = 2 x Pi x Torque / (Swept Volume)>>"Bmep is a useful comparitor of engine performance and state>of tune, although, care must be taken to consider the rpm at>which the engine is operating to determine the power>potential.">>Looks like I'll be changing my guage formula heheh.>Shad I'm not sure what 'Swept Volume' is, displacement? Anyway, this looks appropriate:"BMEP = 150.8 x TORQUE

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Gents,Sorry for the late reply as I was spending the weekend away from home with my girlfriend.I

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Yes there is a significant amount of prop drag. This was most noticable during a practice forced landing. When initiated the instructor, of course, pulled the throttle to idle.But as soon as the student executed the emergency checklist and stated "RPM selector - Feather" they selected +/-3psi to counteract the drag from the propeller turning idle. I think it took about 1 or maybe 2 seconds for the drag to "kick in" but this is reversable as it also takes the engine + prop about 1 to 2 secs to spin up. This was due to the fact that the prop is powered by a free spinning turbine and not by a direct drive.

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> No, that was a regression on BMEP, which applies to>reciprocating engines. >> To indicate relative torque in psi, it appears one should>just take that "Eng1 Torque" (displayed on the C208 panel)>value and multiply by some constant. Max rated torque is near>2000 ft-lb, so if the constant were 0.10, then you would have>a number reading '200 psi' at rated torque. >Which is exactly the formula I first gave :).CheersShad

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Finally had some time to read into the replies more carefully.The only thing I know is that one truly forgets fast. It

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I am attempting this same gauge with the PC-9. Can anyone help me with a value which would give me an accurate torque reading in psi...??

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Ok. I think I have found a work-around for the moment. But now I have another prob. The analogue part of the gauge isn't functioning correctly. The needle spins around 1 full revolution where it should only be moving about 1/4 of a circle. This is my code-(A:ENG1 TORQUE, pound-force per square foot) 1.7 /Any suggestions..??

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Ok. I have narrowed the problem down to the MaskImage. If I get rid of the MaskImage, the needle functions correctly. If the MaskImage is there, the needle spins too much as if were out of scale..???

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